1. Field of the Invention
The present invention relates to medical equipment and, more particularly, to an artificial heart and is used to provide for autonomous and auxiliary circulation in experimental and clinical conditions.
Vital activity is marked by significant changes in the vascular tension and the amount of blood passed through the greater and lesser circulation pumps. Therefore, to control an artificial heart, one has to adjust its rhythm and maintain a constant stroke volume irrespective of variations in the peripheral vascular resistance or the resistance of the pneumatic piping. In doing so, special attention must be paid to the interaction between the right and left pumps of the artificial heart, and utmost care must be taken to avoid the pumping of blood from one circulation to the other, which otherwise may lead to irreversible deposition of blood either in the pulmonary or systemic circulation.
There is known an artificial heart of the type that comprises blood circulating pumps, each having a housing with a diaphragm installed in said housing and dividing it into two chambers, i.e. a hydraulic chamber and a pneumatic chamber. The hydraulic chamber has an inlet valve and an outlet valve incorporated in the blood circulation system. There are known pumps of the type that comprises an instantaneous blood volume transducer of the induction type (cf. US Patent Specification No. 3,491,377, Cl. 3-1, of 1970).
2. Description of Prior Art
Devices of the aforesaid type, comprising an induction transducer to monitor instantaneous blood volume values in the hydraulic chamber, have a number of disadvantages. An artificial heart of this type may fail to function properly due to the effects of external magnetic fields. A non-uniform deflection of the movable part of the pump affects the accuracy of the signal which is proportional to the instantaneous blood volume. The presence of metal components attached to the movable elastic part of the pump (a diaphragm or an elastic bag) tells on the service life of the pump.
Of course, the foregoing type of pump can incorporate a capacitive transducer for monitoring the volume of blood in the hydraulic chamber. It is clear, however, that the capacitive transducer is as disadvantageous as the induction transducer.
There are known artificial heart control systems of the type that comprises sensitive elements accomodated in the right and left pumps. Said elements are sensitive to the volume of blood in the respective pump. Each of said sensitive elements is coupled via a converter and a threshold unit to a unit for setting the duration of compressed gas intake. The latter unit switches an electropneumatic valve through which the gas chamber of a respective pump is alternately connected to compressed and rarefied gas units.
One such system comprises a servovalve controlled by an electronic device (cf. K. W. Hiller, W. Seidel and W. J. Kolff, "An Electronic Mechanical Control for an Intrathoracic Artificial Heart," An. J. Med. Electron., 1963).
This system is disadvantageous in that it calls for an operator to continuously check and balance the deliveries of both pumps in case of changes in the peripheral vascular resistance or serious loss of blood.
The difficulty of adjusting the pressure in the pneumatic chambers is partially overcome in another known device, wherein the stroke volume is adjusted with the aid of diaphragm limit position sensors (cf. M. J. Crossby, "On the Control of Artificial Hearts," Cardiac Engineering, vol. 3, pp. 88-114, 1970).
The latter device is disadvantageous in that it only controls the duration of the compressed gas intake. The complete duration of the diaphragm's motion, which corresponds to the stroke volume, remains uncontrolled, which may lead to an inadequate exchange of blood between the greater and lesser circulations and the pumping of blood to a greater or lesser circulation alone. In addition, the combination of the electrical and mechanical components gives rise to a number of problems which limit the service life of the artificial heart.
There is further known a device which is intended to provide an optimum solution to the problem of improving the selection of time intervals between the onset and end of the delivery and suction phases of each pump (cf. USSR Inventor's Certificate No 434,941, Cl. AG1 F 1/24, granted on an application filed in 1971). This device is disadvantageous in that it only controls the time during which pressure is applied, but not the complete blood delivery and suction time.
On of the basic disadvatages of all of the foregoing devices is the lack of means to maintain equal deliveries of both pumps irrespective of variations in the peripheral vascular resistance or the resistance of the pneumatic lines.
It is an object of the present invention to ensure an equal exchange of blood between the greater and lesser circulations irrespective of changes in the peripheral vascular resistance.
It is another object of the invention to ensure a constant stroke volume of pumps.
It is still another object of the invention to make it possible to balance the exchange of blood between the greater and lesser circulations.
It is yet another object of the invention to make an artificial heart sensitive to the venous return.
It is also an object of the invention to make an artificial heart sensitive to changes in the arterial pressure.
Finally, it is an object of the invention to provide a possibility of visually checking the discharge of air from the hydraulic chamber.